Home heating oil tanks have been around for a very long time, and have hardly changed at all over the last 100 years. There are a few main components that make up a typical oil tank, and we’ll explain how they work together.
The tank itself is generally a welded steel enclosure, with rounded edges top and bottom. This is known as a vertical tank, and the most common size is 275 gallons, followed by the second most common size, 330 gallons. Occasionally, when installed in tight spaces, such as a crawl space, these tanks are used in a Horizontal orientation. In this case, the two flat sides are top and bottom, and the rounded edges are on the sides.
When twin tanks are used, there are two ways that they are set up. The most common setup involves a connector pipe on top of the two tanks. The oil comes in through the fill pipe into the first tank. Once the first tank is filled to the top, the oil is then forced up and out of the first tank, into the second tank. The vent pipe and whistle are in the second tank, so once the level in the second tank rises to the whistle, the driver knows the tanks are full. The tanks are then connected at the bottom via a small oil line which helps the tanks equalize with time.
The second way twin tanks are used is with a separate fill line and vent line in each tank. This gives the driver more control over how much each tank gets.
There is another type of tank, manufactured by ROTH USA, that is a double-walled design – see here.
Fill Pipe / Vent Pipe / Whistle/Vent Alarm
When an oil tank gets filled, the driver connects the hose from the truck to the Fill Pipe on the outside of the house. As soon as the pump is turned on, oil starts flowing into the tank, forcing the air out of the tank through the Vent Pipe. On the inside of the tank, hanging beneath the Vent Pipe, is the Whistle/Vent Alarm. The whistle measures approximately 6 inches long, but can vary in height for different tanks. As the air escapes, it makes an audible whistling sound that the driver can hear from outside the house. Because this whistle hangs down into the tank, as the tank is filled the oil eventually rises and touches it. When this happens, the whistle stops vibrating (and therefore whistling) and the driver knows to shut the pump off. At this point, there is an air space left in the top of the tank, generally about 5-6 inches from the top. This allows for some expansion of the oil as it warms up, and prevents the tank from being over-filled if the pump is not shut off right away.
The float gauge is what most oil tanks are fitted with initially. The float gauge generally has a hinged arm that has a plastic cork-like piece on the end that floats in the oil. As the oil level lowers, the arm lowers with it, and moves the indicator disc on in the vial down accordingly. Float gauges tend to be somewhat correct, but should not be counted on as a precision level indicator. This is because they tend to be one-size fits all, and cannot take into account the curvature of the tanks. They can also get weighed down with sludge over time - see below what the float looks like after several years!
FAQ: Can a Smart Oil Gauge be installed, while keeping the Float Gauge in place? Yes! As long as there is an extra opening in the tank, the Smart Oil Gauge can be installed alongside the float gauge.Oil Feed Lines
The oil feed lines transport the oil from the tank to the burner. These are most commonly affixed to the bottom of the tank, but occasionally come from the top of the tank. The benefit to having the oil feed lines coming from the top of the tank, is the installer can decide how far into the tank to lower the end of the line. By leaving a few inches between the line and the bottom of the tank (imagine a straw that does not reach the bottom of a cup), it is unlikely that any sludge can get sucked up through the lines when the tank gets low. The downside to having the oil feed lines come from the top, is that when the tank gets really low, the burner may shut down even though there is still oil in the tank.